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Adaptive modifications of human postsaccadic pursuit eye movements induced by a step-ramp-ramp paradigm.

The main purpose of the present study was to investigate adaptive properties in human smooth-pursuit eye movements generated by a peripheral moving target. In adaptation trials, a target appeared in the peripheral visual field and immediately moved away at a constant speed, and a subject made a saccade and postsaccadic pursuit responses to track it. The target speed was, however, changed to a higher or lower constant speed (step-ramp-ramp target motion) at the termination of the saccade. This adaptation paradigm induced adaptive modifications in postsaccadic pursuit responses and our results revealed the following properties of the pursuit adaptation system. TOPOGRAPHIC MODIFICATION: Modification of the initial pursuit velocity depends on the position of a moving target. PURSUIT GAIN CHANGE: Pursuit velocity is modified not by the addition of a constant bias to the pre-adaptation pursuit velocity, but by a change in the pursuit gain (pursuit velocity/target velocity). LACK OF INFLUENCE ON SACCADE PROPERTIES: Pursuit adaptation does not change the amplitude and latency of saccades either to a moving target or to a stationary target.

Adaptation, Physiological↗

The stress process perspective and adaptation of people with schizophrenia--an exploratory study.

BACKGROUND: Adaptation of people suffering from schizophrenia still raises numerous questions left unanswered by correlational studies and predictive models. A theoretical framework likely to bring new answers is the stress process perspective. Using the transactional model of coping, to which psychological and social variables have been added, this exploratory research studies the adaptation of 101 people with schizophrenia. METHOD: The research design is correlational with only one crosswise measure. RESULTS: The model predicts 60.7% of variance of adaptation and gives support that the transactional model of coping contributes to this variance. Five variables show a significant effect and account for 48% of the variance, and three interaction effects (two two-way and one three-way) add another 12.7% to the explained variance. CONCLUSION: Results give support to the significant impact of the variables education, age and negative symptoms on adaptation. They highlight the importance of accommodation, a cognitive strategy used by people with schizophrenia to increase their adaptation. They also challenge the broadly accepted assumption of a negative influence of life events on adaptation. Finally, the interaction effects allow us to better understand the mutual effects of variables on adaptation and confirm their relevance.

Adaptation, Psychological↗

Adaptation of the food-borne pathogen Bacillus cereus to carvacrol.

Carvacrol, a natural antimicrobial compound present in the essential oil fraction of oregano and thyme, is bactericidal towards Bacillus cereus. A decrease of the sensitivity of B. cereus towards carvacrol was observed after growth in the presence of non-lethal carvacrol concentrations. A decrease of the melting temperature (Tm) of membranes from 20.5 degrees C to 12.6 degrees C was the immediate effect of the addition of carvacrol. Cells adapted to 0.4 mM carvacrol showed a lower membrane fluidity than nonadapted cells. Adaptation of 0.4 mM carvacrol increased the Tm from 20.5 degrees C to 28.3 degrees C. The addition of carvacrol to cell suspensions of adapted B. cereus cells decreased Tm again to 19.5 degrees C, approximately the same value as for the non-adapted cells in the absence of carvacrol. During adaptation, changes in the fatty acid composition were observed. The relative amount of iso-C13:0, C14:0, and iso-C15:0 increased and cis-C16:1 and C18:0 decreased. The head-group composition also changed, two additional phospholipids were formed and one phospholipid was lacking in the adapted cells. It could be concluded that B. cereus adapts to carvacrol when present at non-lethal concentrations in the growth medium by lowering its membrane fluidity by changing the fatty acid and headgroup composition.

Adaptation, Physiological↗

Sensorimotor adaptation to visual distortions with different kinematic coupling.

We investigated the mechanisms of sensorimotor adaptation by sequentially exposing human subjects to different visual distortions. Subjects performed a manual tracking task, while the relationship between their actual finger movement and its visual feedback was manipulated either by a position-to-position (PP), or by a position-to-velocity (PV) transformation. The outcome confirmed previous findings, in that adaptation to PP facilitated the subsequent adaptation to a second, additional PP. More importantly, our present data documented that pre-exposure to PP interferes with the subsequent adaptation to PV, and vice versa. Thus, we observed anterograde interference between two transformations of common physical nature (i.e., visual), but different kinematic coupling. When previous work on sequential adaptation to visual and mechanical transformations is reconsidered in light of this finding, converging evidence is yielded in favor of a distributed adaptive mechanism, where the magnitude of interference between two successive adaptation sessions depends on the overlap of the involved neural structures.

Adaptation, Ocular↗

Motion adaptation: net duration matters, not continuousness.

Motion processing is strongly adaptable. Adaptation strength generally increases with motion duration. Little is known, though, about the effect of motion onsets and offsets, which might be relevant if adaptation is not based on motion duration per se, but on the recent cumulated activity of motion-processing mechanisms. Thus, we presented intermittent motion with three different onset rates for adaptation. The duty cycle was kept constant at 33% while the rate of motion onsets was either 1.4, 2.8, or 5.6 per second. Stationary stimuli and continuous motion were used as reference conditions. The amplitude of the N2 component of human motion visual evoked potentials was used to quantify adaptation. All three onset rates induced virtually identical amounts of adaptation (occipitally, P=0.71; occipito-temporally, P=0.27), suggesting that the continuousness of the stimulus does not play an important role in motion adaptation. This was confirmed by measuring the motion aftereffect psychophysically.

Adaptation, Physiological↗

The role of eye movements in visuo-manual adaptation.

The present study evaluated the role of eye movements for manual adaptation to reversed vision. Subjects tracked a visual target using a mouse-driven cursor. In Experiment A, they were instructed to look at the target, look at the cursor, fixate straight ahead, or received no instructions regarding eye movements (Groups T, C, F, and N, respectively). Experiment B involved Groups T and C only. In accordance with literature, baseline manual tracking was more accurate when subjects were instructed to move their eyes rather than to fixate straight ahead. In contrast, no such benefit was observed for the adaptive improvement of tracking. We therefore concluded that transfer of information from the oculomotor to the hand motor system enhances the ongoing control of hand movements but not their adaptive modification; probably because the large computational demand of adaptation does not allow an additional processing of supplementary oculomotor signals. We further found adaptation to be worse in T than in any other group. In particular, adaptation was worse in T than in C although eye movements were the same: subjects in both groups moved their eyes in close relationship with the target rather than the cursor, Group C thus disobeying our instructions. The deficient performance of Group T is therefore not related to eye movements per se, but rather to our instructions. We conclude that an independently moving target strongly attracts eye movements independent of instruction (i.e. Groups T and C), but instructions may redirect spatially selective attention (i.e. Group T vs C), and thus influence adaptation.

Adaptation, Physiological↗

The contribution of proprioceptive feedback to sensorimotor adaptation.

It is known that proprioceptive signals from muscles, joints, and skin are involved in the execution of aimed arm movements, but their role in the acquisition of new motor behaviour is largely unknown. Previous research using deafferented patients yielded inconsistent findings: sensorimotor adaptation was found to be less, equal, or even better than in controls. The present study uses a different approach: we degraded proprioceptive signals in healthy subjects by wrist vibration, while leaving them intact in a control group. In order to induce sensorimotor adaptation, both groups executed pointing movements under a visual (Exp. A) or a mechanical perturbation (Exp. B). We found that adaptation to the visual distortion was little affected by vibration, while adaptation to the mechanical distortion was substantially impaired. We conclude that proprioceptive signals which overtly disagree with visual ones (Exp. A) are not used for adaptation, while those which largely agree with visual ones (Exp. B) are used to enhance adaptive recalibration. These results indicate that intact proprioception is needed for mechanical but not for visual adaptation, which implies that the underlying mechanisms are at least partly distinct.

Adaptation, Physiological↗

Concurrent adaptation to opposing visual displacements during an alternating movement.

It has been suggested that, during tasks in which subjects are exposed to a visual rotation of cursor feedback, alternating bimanual adaptation to opposing rotations is as rapid as unimanual adaptation to a single rotation (Bock et al. in Exp Brain Res 162:513-519, 2005). However, that experiment did not test strict alternation of the limbs but short alternate blocks of trials. We have therefore tested adaptation under alternate left/right hand movement with opposing rotations. It was clear that the left and right hand, within the alternating conditions, learnt to adapt to the opposing displacements at a similar rate suggesting that two adaptive states were formed concurrently. We suggest that the separate limbs are used as contextual cues to switch between the relevant adaptive states. However, we found that during online correction the alternating conditions had a significantly slower rate of adaptation in comparison to the unimanual conditions. Control conditions indicate that the results are not directly due the alternation between limbs or to the constant switching of vision between the two eyes. The negative interference may originate from the requirement to dissociate the visual information of these two alternating displacements to allow online control of the two arms.

Adaptation, Physiological↗

The interplay between strategic and adaptive control mechanisms in plastic recalibration of locomotor function.

We have previously shown that viewing simulated rotary self-motion during treadmill locomotion causes immediate strategic modifications (Richards et al. in Presence Teleoper Vir Real 13:371-384, 2004) as well as an after effect reflecting adaptive modification of the control of position and trajectory during over-ground locomotion (Mulavara et al. in Exp Brain Res 166:210-219, 2005). The process of sensorimotor adaptation is comprised of both strategic and adaptive control mechanisms. Strategic control involves cognitive, on-line corrections to motor outputs once one is aware of a sensory discordance. Over an extended period of exposure to the sensory discordance, new strategic sensorimotor coordination patterns are reinforced until they become more automatic, and therefore adaptive in nature. The objective of this study was to investigate how strategic changes in trunk control during exposure to simulated rotary self-motion during treadmill walking influences adaptive modification of locomotor heading direction during over-ground stepping. Subjects (n = 10) walked on a motorized linear treadmill while viewing a wide field-of-view virtual scene for 24 min. The scene was static for the first 4 min and then, for the last 20 min, depicted constant rate self-motion equivalent to walking in a counter-clockwise, circular path around the perimeter of a room. Subjects performed five stepping trials both before and after the exposure period to assess after effects. Results from our previous study showed a significant change in heading direction (HD) during post-exposure step tests that was opposite to the direction in which the scene rotated during the adaptation period. For the present study, we quantified strategic modifications in trunk movement control during scene exposure using normalized root mean square (R(P)) variation of the subject's 3D trunk positions and normalized sum of standard deviations (R (O)) variation of 3D trunk orientations during scene rotation relative to that during static scene presentation. Associated 95% confidence intervals, CI(P) and CI(O), were calculated to investigate the variation of strategic modifications during scene exposure. Repeated measures ANOVA and individual subject regression analyses showed that R(P) and R(O) (i.e. strategic modifications) for trunk fore/aft (X) positions and yaw rotations, respectively, decreased significantly over the exposure period. Furthermore, we found a significant correlation between the magnitude change in HD and the rate at which the variation of strategic modifications in trunk X decreased. We also found evidence of a correlation between HD and the rate at which strategic modifications in trunk yaw decreased. We infer that adaptive recalibration of locomotor trajectory using optic flow stimuli depends on the rate at which kinematic variability associated with strategic control is reduced.

Adaptation, Physiological↗

Dual adaptation to two opposing visuomotor rotations when each is associated with different regions of workspace.

Studies examining dual adaptation to opposing novel environments have yielded contradictory results, with previous evidence supporting both successful dual adaptation and interference leading to poorer adaptive performance. Whether or not interference is observed during dual adaptation appears to be dependent on the method used to allow the performer of the task to distinguish between two novel environments. This experiment tested if colour cues, a separation in workspace, and presentation schedule, could be used to distinguish between two opposing visuomotor rotations and enable dual adaptation. Through the use of a purpose designed manipulandum, each visuomotor rotation was either presented in the same region of workspace and associated with colour cues (Group 1), different regions of workspace in addition to colour cues (Groups 2 and 3) or different regions of workspace only (Groups 4 and 5). We also assessed the effectiveness of the workspace separation with both randomised and alternating presentation schedules (Groups 4 and 5). The results indicated that colour cues were not effective at enabling dual adaptation when each of the visuomotor rotations was associated with the same region of workspace. When associated with different regions of workspace, however, dual adaptation to the opposing rotations was successful regardless of whether colour cues were present or the type of presentation schedule.

Adaptation, Psychological↗

Adaptive and cross-protective responses of Pseudomonas sp. DJ-12 to several aromatics and other stress shocks.

Pseudomonas sp. DJ-12 cells were subjected to mild treatments of stress such as exposure to biphenyl, 4-chlorobiphenyl (4CB), 4-hydroxybenzoate (4HBA), ethanol, and heat, and then were examined for production of stress-shock proteins and morphological changes. The adapted cells were then subjected to lethal stress conditions such as 200 mm 4CB, 100 mm biphenyl, 10 mm 4HBA, 20% ethanol, and 46 degrees C to examine crossly protective responses to the stresses. Several stress-shock proteins including DnaK and GroEL were newly synthesized in the adapted cells. Some of them were commonly produced by those stresses separately treated. The cells treated with these aromatic hydrocarbons showed destructive openings on the cell envelopes. On the other hand, those cells treated with ethanol or heat displayed irregular rod shapes with wrinkled surfaces. The adapted cells to each stress under sublethal conditions exhibited increased resistance to the same stress of lethal conditions. The cells adapted with 5 mm 4HBA showed greater protection for survival than those adapted by other stresses. In addition, those adapted cells showed increased resistance to other stresses as a cross-protection phenomenon. The cells adapted to 42 degrees C exhibited markedly increased resistance to the lethal stresses of 46 degrees C as well as to 20% ethanol.

Adaptation, Physiological↗

Computational nature of human adaptive control during learning of reaching movements in force fields.

Learning to make reaching movements in force fields was used as a paradigm to explore the system architecture of the biological adaptive controller. We compared the performance of a number of candidate control systems that acted on a model of the neuromuscular system of the human arm and asked how well the dynamics of the candidate system compared with the movement characteristics of 16 subjects. We found that control via a supra-spinal system that utilized an adaptive inverse model resulted in dynamics that were similar to that observed in our subjects, but lacked essential characteristics. These characteristics pointed to a different architecture where descending commands were influenced by an adaptive forward model. However, we found that control via a forward model alone also resulted in dynamics that did not match the behavior of the human arm. We considered a third control architecture where a forward model was used in conjunction with an inverse model and found that the resulting dynamics were remarkably similar to that observed in the experimental data. The essential property of this control architecture was that it predicted a complex pattern of near-discontinuities in hand trajectory in the novel force field. A nearly identical pattern was observed in our subjects, suggesting that generation of descending motor commands was likely through a control system architecture that included both adaptive forward and inverse models. We found that as subjects learned to make reaching movements, adaptation rates for the forward and inverse models could be independently estimated and the resulting changes in performance of subjects from movement to movement could be accurately accounted for. Results suggested that the adaptation of the forward model played a dominant role in the motor learning of subjects. After a period of consolidation, the rates of adaptation in the internal models were significantly larger than those observed before the memory had consolidated. This suggested that consolidation of motor memory coincided with freeing of certain computational resources for subsequent learning.

Adaptation, Physiological↗

Skeletal muscle adaptations to prolonged training, overtraining and detraining in horses.

Thirteen standard-bred horses were trained intensively for 34 weeks and detrained for 6 weeks to study skeletal muscle adaptations to prolonged training, overtraining and detraining. Training included endurance (phase 1, 7 weeks), high-intensity (phase 2, 9 weeks) and overload training (OLT) (phase 3, 18 weeks). During phase 3, horses were divided into two groups, OLT and control (C), with OLT horses performing greater intensities and durations of exercise than C horses. Overtraining was evident in OLT horses after week 31 and was defined as a significant reduction in treadmill run time in response to a standardised exercise test (P<0.05). Relationships between peripheral (skeletal muscle) and whole body (maximum O2 uptake, V.O2, max, treadmill run time) adaptations to training were determined. Prolonged training resulted in significant adaptations in morphological characteristics of skeletal muscle but the adaptations were limited and largely completed by 16 weeks of training. Fibre area increased in all fibres while the number of capillaries per fibre increased and the diffusional index (area per capillary) decreased. Mitochondrial volume density continued to increase throughout 34 weeks of training and paralleled increases in V.O2,max and treadmill run time. Significant correlations were noted between mitochondrial volume and V.O2,max (R=0.71), run time and V.O2,max (R=0.83) and mitochondrial volume and run time (R=0.57). We conclude that many of adaptive responses of muscle fibre area and capillarity occur in the initial training period but that markers of oxidative capacity of muscle indicate progressive increases in aerobic capacity with increases in training load. The lack of differences between C and OLT groups indicated that there may be an upper limit to the ability of training stimulus to evoke skeletal muscle adaptive responses. There was no effect of overtraining or detraining on any of the adaptive responses measured.

Adaptation, Physiological↗

Landscape genomics analysis reveals the genetic basis underlying cashmere goats and dairy goats adaptation to frigid environments.

Understanding the genetic mechanism of cold adaptation in cashmere goats and dairy goats is very important to improve their production performance. The purpose of this study was to comprehensively analyze the genetic basis of goat adaptation to cold environments, clarify the impact of environmental factors on genome diversity, and lay the foundation for breeding goat breeds to adapt to climate change. A total of 240 dairy goats were subjected to genome resequencing, and the whole genome sequencing data of 57 individuals from 6 published breeds were incorporated. By integrating multiple approaches such as phylogenetic analysis, population structure analysis, gene flow and population history exploration, selection signal analysis, and genome-environment association analysis, an in-depth investigation was carried out. Phylogenetic analysis unraveled the genetic relationships and differentiation patterns among dairy goats and other goat breeds. Through signal analysis (&#x3b8;&#x3c0;, FST, XP-CLR), we identified numerous candidate genes associated with cold adaptation in dairy goats (STRIP1, ALX3, HTR4, NTRK2, MRPL11, PELI3, DPP3, BBS1) and cashmere goats (MED12L, MARC2, MARC1, DSG3, C6H4orf22, CHD7, MYPN, KIAA0825, MITF). Genome-environment association (GEA) analysis confirmed the link between these genes and environmental factors. Moreover, a detailed analysis of the critical genes C6H4orf22 and STRIP1 demonstrated their significant roles in the geographical variations of cold adaptation and allele frequency differences among different breeds. This study contributes to understanding the genetic basis of cold adaptation, providing crucial theoretical support for precision breeding programs aimed at improving production performance in cold regions by leveraging adaptive alleles, thereby ensuring sustainable animal husbandry.

Environmental adaptation↗

Light and dark adaptation of halorhodopsin.

Dark incubation of envelope vesicles derived from a strain of Halobacterium halobium that lacks bacteriorhodopsin but contains halorhodopsin and a third rhodopsin-like pigment caused a decrease in the flash yield [the amplitude of a transient absorbance change of flash reactive component(s) by flash] of halorhodopsin but not the rhodopsin-like pigment. The flash yield decreased to reach a low steady level after incubation for about 4 days in the dark. The flash yield of halorhodopsin at any stage of dark incubation was increased by actinic illumination of the vesicles. The flash yield at 490 nm (absorbance increase) was found to be approximately proportional to that at 590 nm (absorbance decrease). These results indicate that halorhodopsin in the envelope vesicles has two forms, dark and light adapted, and that the halorhodopsin phototransient absorbing at 490 nm is originated from the light-adapted form. A difference spectrum between these two forms of halorhodopsin shows that the light-adapted halorhodopsin was red-shifted from the dark-adapted form. The light-induced membrane potential was measured by tetraphenylphosphonium uptake. The uptake by the dark-adapted vesicles was slower than that by the light-adapted vesicles, suggesting that only the light-adapted halorhodopsin has ion-transporting activity.

Adaptation, Biological↗

Axotomy-induced temporal dissociation of long-term adaptive changes at neuromuscular synapses of a crayfish phasic motoneuron.

Periodic in situ stimulation of an identified crayfish phasic extensor motoneuron for 3 consecutive days (2 h/day) at 2.5 Hz leads to long-term adaptation (LTA) of its neuromuscular synapses. LTA is characterized by reductions in both initial excitatory postsynaptic potential (EPSP) amplitudes and synaptic depression during repeated stimulation. These adaptive changes were evident 1 day following periodic stimulation. Axotomy of the motoneuron before or after the first day of stimulation of its distal surviving axon abolished both adaptive changes. Axotomy between the second and third stimulation periods abolished only the resistance to synaptic depression. Both adaptive changes were expressed following axotomy after the third day of stimulation. Axotomy alone did not affect neuromuscular transmission in control, unstimulated animals. These results show that axonal continuity between the phasic extensor motoneuron's cell body and its neuromuscular synapses is required at specific times during periodic stimulation for the expression of each of these long-term adaptive changes in neuromuscular transmission. Furthermore, the two adaptive changes in transmission are temporally separable, with the resistance to depression requiring more periodic stimulation to emerge than the reduction in initial EPSP amplitudes. The results also suggest that the molecular components responsible for the expression of these adaptive changes are synthesized in the soma and transported down the axon in response to periodic stimulation of the phasic axon.

Adaptation, Physiological↗

Steady-state analysis of alpha-melanotropin in the pars intermedia of Anolis carolinensis: effect of background adaptation.

The steady-state levels of alpha-melanotropin-stimulating hormone (alpha-MSH)-related peptides were examined in the pars intermedia of the reptile Anolis carolinensis as a function of background adaptation. After a 7-day period, the content of immunoreactive alpha-MSH-related material in the pars intermedia of light-adapted animals was approximately fourfold higher than that of animals maintained on a dark background for the same period. The immunoreactive alpha-MSH-related material present in the pars intermedia of light-adapted and dark-adapted animals was separately analyzed by gel filtration chromatography, reverse-phase HPLC, and cation-exchange chromatography. For light-adapted animals the major form of alpha-MSH had an apparent molecular weight of 1.5 kDa and a net charge of +4 at pH 3.5. Following reverse-phase HPLC this material eluted as a single peak of immunoreactivity with a retention time distinct from that of both mammalian ACTH(1-13)amide and N-acetyl-ACTH(1-13)amide. For dark-adapted animals a peak of alpha-MSH-sized material with an apparent molecular weight of 1.5 kDa was also detected. Following reverse-phase HPLC analysis this material eluted as an apparent single peak of immunoreactivity with a retention time distinct from that of the mammalian standards. Subsequent analysis of this major HPLC peak by cation-exchange chromatography revealed the presence of at least two forms of immunoreactive alpha-MSH. These forms differed in relative proportions. The major peak of immunoreactivity had a net charge of +4, whereas the minor peak had a net charge of +3. The +3 immunoreactive form was not detected to any appreciable degree in light-adapted animals.

Adaptation, Physiological↗

Glycogen repletion and exercise endurance in rats adapted to a high fat diet.

It is well accepted that exercise endurance is directly related to the amount of carbohydrate stored in muscle and that a low carbohydrate diet reduces glycogen storage and exercise performance. However, more recent evidence has shown that when the organism adapts to a high fat diet endurance is not hindered. The present study was designed to test that claim and to further determine if animals adapted to a high fat diet could recover from exhausting exercise and exercise again in spite of carbohydrate deprivation. Fat-adapted (3 to 4 weeks, 78% fat, 1% carbohydrates) rats (FAT) ran (28 m/min, 10% grade) as long as carbohydrate-fed (69% carbohydrates) animals (CHO) (115 v 109 minutes, respectively) in spite of lower pre-exercise glycogen levels in red vastus muscle (36 v 54 mumols/g) and liver (164 v 313 mumols/g) in the FAT group. Following 72 hours of recovery on the FAT diet, glycogen in muscle had replenished to 42 mumols/g (v 52 for CHO) and liver glycogen to 238 mumols/g (v 335 for CHO). The animals were run to exhaustion a second time and run times were again similar (122 v 132 minutes FAT v CHO). When diets were switched after run 1, FAT-adapted animals, which received carbohydrates for 72 hours, restored muscle and liver glycogen (48 and 343 mumols/g, respectively) and then ran longer (144 minutes) than CHO-adapted animals (104 minutes) that ate fat for 72 hours and that had reduced glycogen repletion. We conclude that, in contrast to the classic CHO loading studies in humans that involved acute (72 hours) fat feedings and subsequently reduced endurance, rats adapted to a high fat diet do not have a decrease in endurance capacity even after recovery from previous exhausting work bouts. Part of this adaptation may involve the increased storage and utilization of intramuscular triglycerides (TG) as observed in the present experiment.

Adaptation, Physiological↗